Lipozyme￣(IM)is much more thermostable and resistant to the denaturation by ultrasonic irradiation in organic medium than in aqueous phase.It is not thermoinactivated at a temperature of as high as 85℃ in n-heptane,while in aqueous medium,its enzymatic activity decreases rapidly with the increase of its thermotreatment temperature when the temperature is above 50℃.The more hydrophobic the reaction medium is,the higher is the ability of the enzyme to resist to the denaturation of ultrasonic irradiation. After the treatmemt by ultrasonic irradiation at 140 W for 40 minutes,the hydrolytic activity of Lipozyme￣(IM)decreases by 95. 5% in aqueous medium,in contrast to only 11. 8%in n-hexane.